Strands of glass fibers are produced by pulling several hundred or more tiny molten streams of glass which issue from holes in the bottom of a molten glass tank over a size applying apron to a gathering shoe which groups the fibers together into a strand. This strand then proceeds to a traverse mechanism and winding drum which provides the pulling action which attenuates the molten glass and coils the strand into a package. The fibers are individually separated at the time that they pass over the size applicator, so that the surfaces of the fibers are substantially completely coated before they are drawn together into a strand. This size acts as a lubricant which separates the individual filaments, and if the filaments are not separated by the size, they will scratch each other and break as they are flexed and drawn over guide eyes in the subsequent twisting, weaving, and finishing operations. Starch base sizes have long been used as the base of the coating materials used for separating and lubricating the individual filaments of the strand.
The coiled package that is produced on the winding drum is dried to remove the moisture from the aqueous starch size, and thereafter the strand is uncoiled from the package and is passed over numerous guide eyes which feed the strand onto twist bobbins. As previously indicated, the present invention relates to coatings on fibers that are to be texturized, and this is done by feeding two strands through an air jet which blows apart or separates the filaments of each strand so that the filaments of one strand intermingle with the filaments of the other strand. One of the strands is fed into the jet at a rate faster than the other strand, so that the filaments of the overfed strand are looped to a controlled degree before the filaments of both strands are reunited. Considerable difficulty is experienced in separating the filaments of the strands that are passed through the air jet during the texturizing process, and it has been found that a considerable improvement in the quality of the texturizing strand can be had using the sizes of the present invention instead of the prior art conventional starch size materials.
According to the present invention, it has been determined that a more uniform texturized strand can be produced if the amount of starch base size that is applied to the fibers is kept below that conventionally used for untexturized strands. The amount of starch base solids that are applied to the fibers should be below approximately 0.6% by weight of the coated fibers with optimum results being had at about 0.4% by weight of the coated fibers. It has further been found, however, that conventional starch base sizes will not adequately protect the fibers using such a small amount of size material, and produce excessive fuzz during the twisting operation and breakage of the strand during the texturizing operation. A higher degree of the mutual abrasion between the fibers is encountered during the texturizing operation than is normally encountered in the normal processing of untexturized strands, and in order to protect the fibers during this service, a new and improved type of starch size had to be prepared.
According to principles of the present invention, it has been discovered that an aqueous starch coating on glass fibers in a forming package will leach out sufficient basic materials from the glass fibers to change the pH of the aqueous size coating. It has further been found that most starch materials, and particularly cationic starch materials change viscosity with a change in pH, and that conventional cationic starch materials lose their dispersant power as the pH approaches 7 or above. Where 1% or more of size solids is applied to glass fibers, the change in viscosity of the starch film on the fibers is not critical; but it is critical in applicants' attempts to put less than 1% of starch base coatings onto the fibers. Applicants further discovered that conventional cationic lubricants employ quaternary primary amines, and that quaternary amines cannot be used, since they agglomerate when in thin layers to expose the fibers. This produces fuzz during twisting, and causes the fibers to break during the texturizing operation.
According to further principles of the present invention, it has been discovered that starch materials that are made cationic with a quaternary ammonium radical of a tertiary amine will provide adequate protection of the fibers during twisting and texturizing even though the coatings are present in less than 0.6% by weight--provided that they also include a cationic lubricant that is also made cationic by reason of quaternary ammonium radicals that are practically devoid of primary amines. Emulsified particles of a solid lubricant such as a wax or a gelled oil are preferably also included. It appears that the starch base coating deposits onto the surface of the glass fibers in a bottom layer comprising the cationic starch material, and that the emulsified solid lubricants remain concentrated in the outer surface of the starch base coating to lubricate guide eyes and prevent excessive powdering of the starch. So far as applicants are aware they are the first to produce this type of layered coating which is believed to account for the ability to adequately protect the fibers with less than 0.6% by weight of coating material solids. It is further believed that basic materials are leached out of the fibers to change the pH of prior art cationic starch and cationic lubricant materials after standing, so that they lose their charge, and thereby lose their dispersant powers. This results in an increase in viscosity, and in agglomeration of the starch base materials. It further results in converting the cationic lubricant to a generally nonionic lubricant, and thereby prevents the cationic lubricant from performing its function of attaching to the surface of guide eyes to build up thereon and prevent contact by the glass fibers.